This study is designed to assess the in vivo differentiation of mucus-producing cells in large airways of new born rats. Neonates, from birth through 80 days maturation will be exposed to normal laboratory air, filtered air, and ozone enriched environments with the idea that these conditions will effect cellular differentiation in airways differently. Light and electron microscope and isoelectric focusing techniques will be employed for staging the progressive development of mucus-producing cells and their chemical components. Specific cytochemical techniques for visualization of carbohydrates will be used in both morphological and gel preparations in order to correlate the appearance and development of reactive-components in each. The data should provide information on how the whole environments as well as specific environmental components effect cellular differentiation in airway epithelium.